DIY heat blankets and temperature control
Quotes are verbatim and attributed to their original authors.
Applied heat cures epoxy faster, harder, and more completely, and lets builders use heat-cured resins. A silicone heater blanket held at temperature by a PID controller is the standard. Store-bought blankets (e.g. from MEI or overseas suppliers) are common, but many builders build their own from resistance wire, fibreglass, and silicone rubber.
Building a blanket
The reliable method is to lay the resistance wire out in an even serpentine using nails as a jig, tape it to a glass mat, and embed it in silicone.
For silicone, builders name suppliers such as Diversified Silicone and "Eager Polymers in Chicago… the silicones inc P45 high temp silicone rubber." High-temperature lead wire is worth using at the connections.
Wattage and power
Blanket output is just watts, and it is set by the wire and voltage:
To dial the temperature, regulate the power with a dimmer, not the voltage:
Fire safety
The most-repeated warning: the adhesive on the tape can ignite before the blanket is embedded in silicone. One builder testing a bare mat found "the glue of the glass tape started to burn in an area of 30cm." Test-run at low power, keep a dimmer in line, and never leave a homemade blanket unattended.
Control: PID and thermocouple
A PID controller with a type-K thermocouple holds the set temperature. The most common gotcha is reversed thermocouple polarity, which makes the reading count down:
Ramp/soak controllers let you program a gentle ramp, a hold at temperature, and a controlled cool-down; builders monitor to a set temperature (e.g. pull the cassette at ~50 °C). Watch current draw against your circuit — homemade blankets in the 1,400–1,800 W range on a 15 A outlet are typical.